A portable contactless interface device used as a computer mouse is known from International Patent No. WO 96/34333. In its preferred described embodiment, this document proposes integrating this interface device between a user and the computer in a ring. In its top portion, the ring includes a first protruding part forming a housing for an electronic circuit and including at its surface a directional antenna. In the front lateral portion there is a second protruding part in which is arranged a two dimensional force sensor used to actuate a computer cursor. Moreover, another force sensor is provided in the bottom portion to select objects on the screen or to carry out commands relating to these objects. Such an action is referred to hereinafter as a “click”. With reference to FIGS. 2 and 3 and the corresponding description of this document, it is clear that the sensor provided for moving the computer cursor is formed by a two dimensional force sensor actuated by the user's thumb. This force sensor allows the cursor to be moved along two perpendicular directions shown in FIG. 2. The force sensor thus determines in which of the four directions given in FIG. 2 the thumb force is exerted in the plane of the sensor. It will be noted that such a force sensor for actuating a cursor firstly limits the precision of the cursor's movement and it is not easy to use given that the ring undergoes movement on the finger, the skin of the finger experiencing relatively significant movements. Thus, a mechanical stress is exerted on the finger and the ring moves when a force is applied by the thumb in one of directions of the sensor plane. It is thus clear that control of the cursor is hampered by these movements of the ring and that this is also uncomfortable for the user.
As an alternative, which may be envisaged, International Patent No. WO 96/34333 mentions that it is possible to arrange adjacent sensors on the ring in place of the two dimensional force sensor so that the direction of movement of the cursor is determined by the sequential actuation of the adjacent sensors. This unclear and largely insufficient teaching does not enable those skilled in the art to understand how to make these adjacent sensors and how to use them to control a computer cursor properly. Moreover, the small dimensions of the ring shown in this document seem greatly to compromise such an embodiment. Those skilled in the art may find in U.S. Pat. No. 5,481,265 a similar device wherein a member is provided which can be actuated by the thumb to control a computer cursor along two orthogonal directions. This member includes four independent regions forming four adjacent force sensors which may be actuated in succession by the thumb to move the cursor up, to the right, down or to the left. According to a variant, these four pressure sensors allow the cursor to be moved to one of the four corners of the computer screen (see FIGS. 7a and 12). This device is not at all easy to use given the position required for the thumb. Moreover, the selective application of a force on the four aforementioned pressure sensors is not easy, and is even impaired. Thus, control of the cursor's movement is approximate and in any case limited as is clear from the description of U.S. Pat. No. 5,481,265.